Dynamo.



E. M. TORMIN.

DYNAMO.

APPLICATION FILED JAR.27,1912.

Patented Aug. 18, 19M

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EGMONT llIAX TORMIN', OF NEWTON CENTER. MASSACHUSETTS, ASSIGNOR T0 HOLTZEE CABOT ELECTRIC COMPANY, (3F BROOKLINE. MASSAQHUSETTS.

DYNAM&

Specification of Letters Patent.

Patented Aug. 18, 1914.

Application filed January 27, 1912. Serial No. 873,724.

To all whom it may concern:

Be it known that I, EGMONT M. Toni-um, a subject of the German Emperor,- and a resident of Newton Center, in the county of Middlesex and State of Massachusetts, have invented a new and useful Improvement in Dynamos, of which the following is a specification.

The present invention relates toldynamo electric machines and more especially to direct-current lighting machines.

The principal'object of my invention is to provide a self-regulating variablespeed dynamo, which may be subjected with impunity to excessively high rotational speeds and which is especially adapted to be driven by a motor vehicle such as an automobile for generating current for the lamps and other electrically-actuated devices carried thereby. Preferably av storage battery is floated on the line that is, connected across the external circuit; and a speed-conltrolled cut-out provided," whereby the external circuit is held open until the dynamo attains a certain minimum speed of rotation,

ually rise as the speed of rotation of the armature or the" rate of travel of the motor vehicle increases until acertain critical speed or rate of travel has been reached beyond which [the current output will no longer increase and may in fact decrease. This is' the essence of my invention. Inasmuch as the armature of a motor-vehicle lighting-dynamo is often subjected to excessi'vely high rotational speeds, it is absolutely necessary that means he provided to prevent the. current output from increasing with such armature speed beyond a certain critical point, for otherwise the machine would be burnt out by the excessive current generated.

Heretofore it has been proposed to em. ploy centrifugally-operating devices whereby the speed of the armature was rendered independent of the rate of vehicle travel and was prevented from increasing beyond certain maximum; but such devices were subject to certain limitations and objections. By means of the present invention they may be eliminated because my dynamo is so arranged that beyond a maximum speed the current output is rendered practically inde pendent of the rate of our travel.

An illustrative embodiment of my invention is shown in the drawings which accompany and form a part of this specification.

In the drawings -Figure 1 is a longitudinal section of a dynamo constructed in accordance with the present invention, Fig., 2 is a transverse section taken on the line 22 of Fig. 1,- Fig. 3 is an elevation of the pole piece, lfiig. 4 is a. diagram showing the distribution of the magnetic flux in the usual bipolar machine, when the armaturei 75 is stationary and the fields separately cited, and Fig. 5 is a diagram showing the distribution under similar conditions of the magnetic flux in my improved machine.

In the particular drawings selected for more fully disclosing the principle of my invention, 1 a shaft suitably journaled in the frame 4 and carrying the armature core 2, which. is preferably laminated and which may be provided with the slots}. Secured to the shaft are the commutator 5 and the speed-controlled cut-out 6, sueh as described in my divisional application above r ferred to.

The field magnet 7, preferably laminated and consisting as shown; in the'present instance of soft iron disks held together by the rivet 7 is secured to the frame in any suitable manner, asfor example, by the bolts 8, and it carries the winding 9 which preferably is a shunt winding. Pole-pieces 10, herein shown as solid, are secured to the field-n'iagnet in any suitable manner, as for example by the bolts 11. The two polepieces 10, 10 are separated preferably by the narror gaps 152, 12, the peripheral length of each of which is small with respect to the circumferential length of the pole-pieces themselves. T he gaps as shown in Fig. 3

maybe inclined with respect tothe axis ofthe machine for the purpose hereinafter more fully set forth. The angle :10 subtended by the peripheral length of one of the gaps 12 is equal to, or preferably as shown, smaller than the an le of commutation 3 2'. 6., the angle su'tended by the peripheral length. of a commutator brush (see Fig. 2) so that a plurality of armature coils is short-circuited under the pole-pieces in a strong magnetic field by the brushes, and therefore the back electromotivc force developed at their terminals by such short circuiting is greater than if they were shortcircuited in a practically zero field as has heretofore been customary.

As is well understood, in the oi-polar dynamo of the prior art, the neutral line which is the line joining the neutral points, or the points at which the brushes must be placed for minimumsparking, is not exactly at right angles to' the line joining the centers of the pole-piecesybut-is shifted a few degrees from such central line in thedirection of rotation on account of the conccntration of the fieId'Under-the leading pole-tip and its weakening under the trailing pole-tip. In such machines; each f'polepiece does not in general subtend at an an-- gle greater than from ninety to one hundred and twenty degrees, so that the angle subtended by the peripheral length of each gap between. the pole-pieces is usually relatively large, the peripheral length of such gap bemg comparable to the circumferential length of the pole-pieces themselves and the angle subtended by such peripheral length of said gap being-of course very much larger than the angle of commutation. An example of this construction is shown diagrammatically in Fig. l, in which a, a, represent the pole pier-cs and Z; the armature. The distribution of the lines of force when the armature is at rest and the field separately excited is rcpresented by the lines 0. It will be seen that the line 'rw n is the neutral line above referred to and that there is practically no flux in the gaps c-f, e--f, between the leading pole-tip of one pole of the trailing,

polc-tip f of the other. Therefore when the brushes are placed at points a few degrees beyond the neutral points in the direction of rotation, practically sparkless commutation may be obtained because there isa practically zero magnetic flux at these points, and hence practically no current flowing in the coils at the moment they are short-circuited by the brushes. For this reason, practically no back electromotive force is developed at the terminals of the short-circuited' coils during commutation. In such a machine the current output. caetem's paribua, is substantially a linear function of the speed of rotation of the armature, the clectromotive force increasing directly with the relative motion between the armature coils and the flux lines, 216., the rate of cutting, and such back electromotive force as is developed in the short-circuited coils during commutation correspondingly but not disproportionately increasing. In my improved dynamo, however, I so arrange matters that the coils shall be short-circuited by the brushes an intense magnetic field, so that there shall be a relatively large current in each coil at the beginning of commutation and a relatively large reverse current therein at the end of commutation, and therefore a relatively large back electromotive force developed at the tcrminals of such coils during commutation. The back electromotive force in my variable speed machine is produced in the same way as in constant speed machines and other direct current generators, namely, by the closing and opening of the coil circuit every time the segments to which the terminals'of such coil are connected make and break contact with a brush and by the inductive elfect due to decrease, reversal, and increaseof current in the coil during commutation. Inasmuch as this back electromative force opposes the direct electromotive' force, it cuts down the current output of the machine. As the rotational speed of the armature israised, thecurrent increases but not proportionately withsuch increase in speed, the current increase being very gradual as the armature speed approaches the critical point, and after the critical point has been passed the back electromotive force increases at a more rapid rate than the direct electromotive force, thereby preventingany further increase-in current strength and keeping such strength practically constant or, when excessive speeds are attained, gradually reducing the same.

As above stated, a battery is preferably connected across the line and the voltage across the brushes istherefore nearly constant at all speeds. In such case the back no electromotive force alone rises as the'velocity of the armature increases and becomes unusually high for high velocities, therebyl keeping the current outputcf the dynamo practically constant, or even causing the same to fall oil for excessively high speeds beyond the critical speed above referred to.

It will be understood of course that it is by no means necessary to employ a battery connected across the line in order to accomplish the object of my'in'vention.

The manner-in whichl am enabled to i11- tensify thebackelectromotive force developed at the terminals of a short-circuited coil during commutation may be more fully 25 explained by reference. to Fig. 5. It will be seen that the spaces c-'f, -e'--f' are almost completely occupied 'by the pole-pieces 10 and that there exists between said poleieces but a narrow 'gap lfi, the peripheral length of which is very much smaller than the circumferential length of the pole-pieces and that the angle subtended by the peripheral length of each gap is very much smaller than the angle of commutation 3 so that in the crmnmtatiou zone. there exists a strong magnetic liux l \Yliidit enters tl'ie armature by way of one polepiece and leaves it by way ot the other.

inasmuch as the air-gap oi the tween the armature and pole piece is much smaller than one-half the length of the gap 12 between the pole-pieces. as clearly shown in Fig. 2. the reluctance oi the circuit a ross thegaps 12 is greater than that i'roxn one tip to the armature to the other tip, and hile there may in fact he a certain small amount of leakage acr ss the tips, such leakage Will not materially allect the creation of an intense magnetic field in the commutation Zone as distinguished from the practically zero field in such zone as shown in Fig. 4. However, as above pointed out, for sparhless commutation it is necessary to place the brushrs at the neutral points of zero or practically zero flux, and inasmuch as the brushes 40 in the present case are located at points where the flux is intense. undue and in fact destructive sparking would take place at said brushes during commutation unless suit able precautions were taken to prevent; or minimize the same. In order to reduce such sparking l preferably provide the armature with a relatively large number of coils, for example, fifty, so that by virtue of this large subdivision, a comparativel small counter electromotive force will be, developed at the terminals of each coil on short-circuit and a relatively small and practically harmless spark be thereby created between the brushes and the armature segments with which the coil undergoing commutation is connected. If the total electromotive force of the niachine measured across the brushes, be divided among fifty coils, the electromotive force as well the counter electromotive force per coil will be only half as great as if twenty-five coils were used, only one-fifth as great as if the armature Were wound. with ten coils, and so on. On account of this high subdivision, a c janparatively large number of commutator segments, for example, many as four, Will simultaneously be in electrical. contact with each brush. This isn'eiideret'l necessary because a narrower brush, for example one spanning only two segments, would not, have a sufiiciently large, crosssection to carry the current out put. In this case a. relatively large number of armature coils, many as three, are simultaneously short-cireuited. By means of this large sub-division of the armature winding. s 'iarking at the brushes reduced below the danger point, being in Fact practically eliminated. Quch reduction or elimigap' bei nation of sparking ated by the use of the Wide brush necessarily tnuployctl. which lengthens the time the coil is undergoing commutation. for the amount of sparking produced on commutation is Well known to e an inverse function vi the time during \rhich a coil remalir- -t-rrt ir -ui d. if the gaps 12 were paralici iitli the axis of" the, armature and tinwe with the arimilxuce slots .3. the smith ,assage of ea h slot with its included c il across the trap 12 would produce loud humming; noise; but by placing: the armature slots and said gaps at an angle with ea-h oi as for example by inclining the gap mm in Fig. l"), a portion only of each wording is under a 'gap as shown at ii. and thu. by the gradual pt ssag'e of an armature winding" acro s the gap, the humming noise above referred to is eliminated.

it will be understood that I do not limit myself to the particular cl'nbodizncnt of my invention which I have described and illus trated, inasmuch as various modifications may be made by those skilled in the art in the ttpl lfll'tlt lls specifically described Without departing from the principle of my inrcir tion; but

Having: thus described one illustrative embodii'u nt of my invention, ivi'hout, how ever, limiting the same thereto. What I claim as new and t tsire to secure by Letters Pat-- cut is- 1. In a direct current dynamo electric machine, a tield magnet and pole pieces secured thereto. the pole pieces being sepa rated by narrow raps, oi uhitli the peripheral length is very vshort compared to the circumference olTsaid pole pieces and said gaps being inclined to the axis. of the ina-- chine.

2. In a variable speed dynamo electric machine. the combination with a field mag net having pole-pieces and nit-ans for di rectinu' a portion of the magnetic flux developed by 1lltl liehl-u'iaguct into the comnmtation zone. of brush es hax'ng the minimum cross-sectional area required to carry the current output and an armature having: such a relatively large number of coils that a con'iparativelv large number thereof will be shiniltanetat--i short-circuitcd by said l-iwishesthc angle subtended by the peripheral length of the gaps between said polepieccs bcin g equal to or smaller than the angle of comn'iutation.

3. In a variable speed dynanio electric niachiuc. comprising means whereby the current output for rotational speeds of the armature beyond a given critical speed is either constant or decreases with such speed of rotation. the combination with brushes ha ving the minimum cross-sectional area re quired to carry the current output and an armature having such a relatively large number of coils that a comparatively large number thereof will be simultaneously shortrircnited by said brushes of a fieldmagnet having pole-pieces, the angle subtended by the peripheral length of the gaps between said gole-pieces being equal to or smaller than t e angle of commutation.

In testimony whereof, I have hereunto subscribed my name this 22nd day of J anuary, 1912.

EGMON T MAX TORMIN. Witnesses:

T. W. NEss, Bow. 0. Nmwcoms. 

